The present invention relates to the production of food products, and, more particularly, to the production of products having at least an outer layer of a material which is heat liquified in the formation of the product and which crystallizes upon cooling to provide a glossy surface.
In the manufacturing of products which are formed of, or coated with, a material which crystallize upon cooling, great care must be exercised to properly cool the products so that the structure of the surface layer is composed of small crystals which provide the desired high quality surface gloss. The materials which require such careful treatment include chocolate, compounds which are a blend of cocoa, sugar and a hard butter, and icings. A consistently high quality smooth glossy surface can be achieved by allowing the products too cool at room temperature until the surface has solidified. Under these conditions, the crystallizing material cools slowly and evenly so that crystal formation begins simultaneously over the entire surface. The growth of each crystal is thus limited by the presence of surrounding crystals and the entire surface develops a structure of small crystals. The slow cooling allows most of the heat within the interior of the material to escape before the surface crystallizes so that the heat remaining after this crystallization is insufficient to remelt and thereby alter the surface structure.
Room temperature cooling, however, requires a long time period during which the product cannot be handled and therefore is economically impractical. It has been standard practice therefore to use a cooling tunnel to rapidly cool the product sufficiently to cause the surface to harden to an extent which permits the products to be packaged. The temperature in the cooling tunnel is typically about 40.degree. F at the central portion thereof and about 60.degree. to 70.degree. F at the entrance end so that the products are not subjected to rapid temperature changes during crystal formation. The products are carried through the cooling tunnel on a conveyor and are within the tunnel for a short period of time, for example 6 to 9 minutes.
The degree to which products can be cooled in a conventional cooling tunnel during a specified period of time is limited. If the temperature within the tunnel is decreased substantially, large crystals form, producing a dull finish. Also, the material hardens too much, decreasing its ability to conduct heat so that the flow of heat from the interior regions of the product is retarded. The surface material, therefore, may crack as a result of the stressess produced by the temperature differential between the surface and the interior regions. Also, if the surface of the product, when it leaves the tunnel, is at a temperature below the dew point of the air in the packaging area, moisture will condense on the coating and mar the surface gloss.
In materials containing crystallizing fats or butters, the packaged products must be stored in a mildly cool environment (for example at 60.degree.F) for an extended period of time (for example 24 hours) to remove the heat from the interior regions of the material gradually. The heat must be removed at a rate which is sufficient to inhibit remelting of the surface but will not unduly harden the surface before the heat is removed so as to trap the heat within the product. With fat containing materials, the entire cooling process must be conducted with particular care to obtain a high quality surface. If there is insufficient cooling of the product interior in the cooling tunnel, or if the packaged product is not promptly placed in cool storage, the internal heat will remelt portions of the surface. Likewise, if the temperature within the tunnel is too low, excessive hardening of the outer layer traps heat within the product causing subsequent melting of the surface.
Remelting of the crystallized surface allows the fat to form larger globules which, upon subsequent cooling, form large fat crystals to product the whitish discoloration of fat bloom.
The present invention utilizes a corona current or electric wind (as it is sometimes called) in such a manner that a high gloss surface is produced and retained on crystalline surface products. In the past, it has been suggested that corona current can be used to cool metal in machining operations (U.S. Pat. No. 3,670,606), to accelerate the baking of bread (Canadian Pat. No. 783,385), and to cool hot loaves of bread (Chemistry and Industry, Oct. 23, 1971, p 1225). However the use of corona current as suggested by these disclosures results in a rough and dull surface when applied to a crystallizing material of the type under discussion.